In understanding the mechanisms of pathological retinal angiogenesis, we have discovered that besides VEGFA, VEGFB, VEGFC, DLL4 and cleaved NOTCH1 induction, hypoxia activates CREB and STAT3 in the mouse retina in a robust and sustained manner. Interestingly enough, blockade of either CREB or STAT3 inhibits VEGFC and FGF2-induced expression of DLL4 and cleaved NOTCH1 in HRMVECs. A large number of studies suggest that NOTCH signaling by modulating the tip versus stalk cell differentiation plays a pivotal role in developmental and postnatal angiogenesis. CREB belongs to a basic/leucine zipper (bZIP) family of transcriptional factors and possess the ability to bind o the consensus sequence TGAC/GTCA in the promoter regions of genes enhancing their expression in response to a wide variety of stimulants, including cytokines, growth factors and hormones and is involved in the regulation of neuronal plasticity, long-term memory and cellular metabolism. Similarly, STAT3, which belongs to a family of transcriptional factors and whose activity is regulated by Tyr/Ser phosphorylation and acetylation, possess the ability to bind to th consensus sequence TTCCGGGAA in the promoter regions of genes inducing their expression in response to a large spectrum of stimulants, including cytokines, growth factors and hormones and is involved in the modulation of cellular growth and migration. While a large body of data demonstrates the importance of these transcriptional factors in the regulation of many cellular processes, including cell proliferation, migration and differentiation, literally nothing is known n regard to their role in the regulation of pathological retinal angiogenesis, particularly in concer with NOTCH signaling. Based on our novel preliminary observations, we hypothesize that CREB and STAT3 via enhancing the expression of DLL4 and thereby NOTCH1 signaling mediates pathological retinal neovascularization. To address this hypothesis, we will test the following three specific aims: Aim 1. To test the hypothesis that CREB mediates hypoxia-induced pathological retinal neovascularization. Aim 2. To test the hypothesis that STAT3 mediates hypoxia-induced pathological retinal neovascularization. Aim 3. To test the hypothesis that hypoxia induces DLL4-NOTCH1 signaling via CREB and STAT3 leading to leaky and non- patterning pathological retinal neovascularization. The execution of the experiments proposed in this grant application should provide us novel information on the upstream mechanisms of NOTCH signaling activation in mediating pathological retinal neovascularization and such knowledge would be useful in the development of therapeutic drugs against this debilitating ocular disease.